Malleable cast iron



Patented Feb. 9, 1943 MALLEABLE CAST IRON Nicholas A. Ziegler and HomerW. Northrup, Chicago, lll., assignors to Crane Co., Chicago, Ill., acorporation of Illinois 'Application December 4, 1941, serial Np.421,585

4 claims. (ol

' namely, good machinability, ductility, tensile This invention relatesto the improvement in the group of alloys suitable 'for making malleableiron castings, which after being subjected to a suitable malleableizingheat treatment will possess a tensile strength and yield point inaccordance with the highest commercial standards and ductility,expressed in terms of percentage elongation, superior to that found inconventional material not treated in accordance with our intion.

A further object is the acceleration of the annealing rate by theaddition of an element which will affect the rate of annealing and atthe same time improve the physical properties of the final malleableiron casting.

established malleableizing practice and method outlined herein.

Malleable iron is first produced as a white iron with practically allits carbon in the combined form. It is rendered soft and ductile byannealing for prolonged vperiods at temperatures cusomarily in theneghborhood of 1560-1850 degrees Fahrenheit to cause the undissolvedcombined carbon or iron carbide to change to graphite; then followscooling to a temperature in the vicinity of the critical range. 'I'hefinal product sought is a microstructure consisting of rounded particlesof temper carbon (graphite) embedded in a soft iron matrix. l

The annealing process is by far the most time-consuming and thereforethe most costly operation in the production of malleable iron castings,and consequently many attempts have been made to reduce the timerequired for the annealing cycle without sacrificing the tradiduction ofa high-quality malleable cast iron by the addition of a small amount ofberyllium to obstruct the formation of flake graphite in the white iron,and by employing an annealing cycle less time-consuming than theprior-art processes.

It is well known that silicon (aswell as other graphite 'formers" likecopper or nickel) promotes the formation of graphite. This is` equallytrue regarding the formation of (1) flake graphite during thesolidication period, resulting in a product known as "gray iron, and (2)"temper carbon during the annealing or malleableizing of originallywhite iron, resulting in a product known as malleable iron. It isequally well known that manganese (as well as other carbide formers likechromium, molybdenum, tungsten, etc.) acts in exactly oppositedirection, i. e. retards the formation of graphite and promotes theformation of combined carbon or carbide. I n the art of manufacturingmalleable castings it thus becomes necessary to balance silicon andmanganese so that upon solidication no free or flake graphite would beformed and al1 carbon would be present in combined form as carbides. Atthe same time these carbides should be suficiently unstable so that uponrehe'ating to the malleableizing temperatures they would break up orgraphitize into temper carbon in reasonably short time periods. Thus itis always desirable to have in the malleable iron as much silicon as ispermissible without developing flake graphite in the original (white)castings during the solidication period. It hasbeen shown by variousinvestigators that silicon greatly accelerates the malleableizingprocess (formation of temper carbon) by increasing the number oftemper-graphite particles per unit volume, thereby reducing the distancethe carbon has to diiuse before precipitating as graphite. It also hasbeen shown that the malleableizing rate is accelerated not only by theease of graphite nucleus formation and the mobility of the carbon atom.but is also inuenced by the relative stability of the original combinedcarbon (carbides). In other words, it is desirable to add to the moltenwhite iron some material which would stabilize and promote formation ofcombined carbon (carbides) upon solidication, but, at the same time,during the malleableizing heat treatment, would not interfere with (andpreferably would promote) breaking up of these carbides and formation oftemper carbon. An outstanding example of an element which functions inthis manner is tellurium.

We have discovered that by the introduction of up'to 0.2% of berylliuminto the molten metal,

the annealing process will be accelerated and the formation of tempercarbon facilitated. As an indication of the favorable eiect upon thephysical properties of the product expressed in positive terms let usconsider the results. obtained with regard to per cent elongation.

It is well known that in malleable iron the desired ductility, expressedas elongation, is a more diiiicult property to develop than the tensilestrength or the yield point. We have found that adding small buteffective amounts of beryllium to white iron considerably improves theductility of the metal after the malleableizing' annealing and alsoallows a simplified and shortened malleableizing treatment to beemployed.

A series of experimental melts were prepared to which were added thespecified amounts' of beryllium or a copper-base alloy containing beryllium. Several test bars were taken from each heat and subjected to acertain malleableizing heat treating cycleyafter which the test barswere subjected to the standard tensile tests. In

, each group of test bars thus treated, two'test bars made of ordinarycommercial cupola white iron were included and tested in parallel withthe copper-beryllium treated irons.

Explanation is made in the upper right hand corner of the drawing of thetreatment or composition of each of the samples.

More specifically, we have discovered the following composition andpercentage ranges to be satisfactory:

Silicon per cent.. .5 to 2.5 Manganese do .3 to 1.0 Sulphur per centmaximum-- .2

Phosphorus do .4

Carbon per cent 1.5 to 3.5 Beryllium do Trace to .2 Iron The remainder'Ihe beryllium is preferably added as a copperbase alloy containingberyllium in amounts up to 4%.

Several different heat treating cycles were thus tried, but-in view ofthe fact thatthe copperberyllium treated irons inevitably had physicalproperties superior to those of the ordinary cupola malleable iron,malleableized together with the former-the test data presented here aretaken from only two representative cycles.

The program of the first run was: heated to 1800 F. in 6 hours; held at1800 F. for l2 hours; cooled to 1500 F. in 2 hours; held at 1500 F. for4 hours; cooled to 1380 F. in 2 hours; held at 1380 F. for 4 hours;cooled to 1300 F. in one hour; held at 1300 F. for 4 hours; cooled to1250 F. in one hour; held at 1250u F. for 4 hours; cooled to 600 F.'withthe furnace and air cooled to room temperature.

Table 1 gives the compositions of the test bars andthe results ofthestandard tests of the bars thus` prepared and treated, together withthe same data for the industrial heat of ordinary commercial cupolamalleable iron. The accompanying drawing is a graphic representation ofThe accompanying drawing shows a superi0 the data presented in thetables.

Table 1 I Nominal chemical analysis Physical properties Composition No.Ilgeat f. Remarks Si Mn s P T C Alloyorelement Tensile Yield Elonadded 1strength point -gation LbaJ Lba,/ Per cent Per cent Per cent Per centPer cent sq. in. sq. in. Per cent 1 5831 0.01 0. 41 0.15 0. 11 3.14 5&%2:3 }mdusrria1hea1 14 241s 1.12 0.41 0.14 0.13 2.08 0.5% C11-Be auoy 22%Alzded 0.1111175 orcue 8 Oy C011- taining 47 Be. 15 2421 1. as 0.35 0.120.13 2.05 0.5% C11-ne a110y 2,31% gg g2g o 16 2420 0.05 0.38 0.13 0.152.96 1.0% C11-Be auoy gg mieduroa, ortog- 1 ea oy con a ing 47 Be.` 11.;2423 1.22 0.35 0.12 0.14 2.72 1.0% cunea11oy.{ gggg 31% 23 a y minderto'demonsnrate that it 1s the beryllium an'dnotthe copper hat isbeneiai, in Table 2 the propertiesof an iron are shown to which onlycopperw'asiagded (compositions #18 and #19 in Table 2) in parallel withthe properties of an industrial malleable iron and those of twocompositions to whichcopper-beryllium master alloy has been added. Allthe members of thislgroup of specimens were subjected to the followingmalleableizing cycle: heated ,to 1880 F. in 6 hours; held at 1800 F. for5 hours; furnace cooled to 1250 F. in 10 hours; furnace cooled to 600 F.air cooled to room temperature.

Table 2 Nominal chemical analysis Physical properties Composition No.11%? Au i 1 t T l Y' 1d El Remarks oy ng e amen ensi e 1e anga- S Mn s PTC' added strength point tion Lba/ Lba/ Per cent Per cent Per cent Percent Per cent Per cent aq. m. aq. in.. 1 5531 0.01 0.41 0.15 0.11 3.14621% 23 }111dustria1het.

,400 41,100 5.5 Add (1057() B 14 271s 1.12 0.41 0.14 0.13 2.08 v 00,50041,300 5.5 e 0 1 e .15 2721 1.33 0.35 0.12 0.13 2.05 }5% C Beanoyl01.000 40,200 5.5 gosecmtammg 452s a 1 Added 1.0% Cu-Be 2426 1.05 0.380.13 0.15 2.96 56 400 ,000 8,0 17 2423 1.22 0.35 0.12 0.14 2.72-}1% C B"auy-l 571700 33.100 0.0 osl'seconalmng a .2 1 C t 59.533- gm g-g C.....1y ...1.1.4.- 10 2305 1.30 0.31 0.13 0.12 .64 u 62,200 37,200 3 5 Itis clear that while the specimens containing copper and beryllium becameductile (that is, developed over 5% elongation) in a 15-hour anneal,similar specimens containing copper without beryllium, under similarconditions, developed only 3.5% maximum elongation.

Referring again to Table l, it may be seen that each composition thererepresented, with the exception of #1, industrial heat, developed betterthan 5% elongation after a heat treatment of only about 40 hoursduration.

Referring to Table 2, it may be seen that each composition thererepresented, with the exception of #1, industrial heat, and' #18 and#19, heats treated with copper, developed better than 5% elongationafter a heat treatment of only about hours duration.

While We have described our invention by referring to certain practicalembodiments in order that a clear disclosure may be made to thoseskilled in the art, it Will be understood that the scope of ourinvention is not to be limited except as may be required by thefollowing claims.

We claim:

1. A white cast iron comprising the following elements as essentialconstituents in approximately the proportions given: si1icon0.52.5%,manganese 0.31.0%, sulphur 0.2% maximum, phosphorus 0.4% maximum,.carbon1.5-3.5%, to

' in approximately the proportions given: silicon 0.5-2.5 manganese0.31.0%, sulphur 0.2% maximum, phosphorus 0.4% maximum, carbon 1.53.5%,to which a copper-base alloy, containl ing beryllium in amounts up to4.0%, is added in amounts from a trace up to 5.0%, the remainder beingiron.

4. A malleableized white cast iron comprising the following elements asessential constituents in approximately the proportions given: silicon0.5-2.5%, manganese 0.31.0%, sulphur 0.2% maximum, phosphorus 0.4%maximum, carbon 1.5-3.5%, to which beryllium is added in amounts from atrace up to 0.2%, the remainder being iron.

NICHOLAS A. ZIEGLER. HOMER W. NORTHRUP.

